IC 418: THE "SPIROGRAPH" NEBULA

Glowing like a multi-faceted jewel,
the planetary nebula IC 418 lies about 2,000 light-years
from Earth in the direction of the constellation
Lepus. This photograph is one of the latest from
NASA's Hubble Space Telescope, obtained with the
Wide Field Planetary Camera 2.

A planetary nebula represents the
final stage in the evolution of a star similar to
our Sun. The star at the center of IC 418 was a
red giant a few thousand years ago, but then ejected
its outer layers into space to form the nebula,
which has now expanded to a diameter of about 0.2
light-year. The stellar remnant at the center is
the hot core of the red giant, from which ultraviolet
radiation floods out into the surrounding gas, causing
it to fluoresce. Over the next several thousand
years, the nebula will gradually disperse into space,
and then the star will cool and fade away for billions
of years as a white dwarf. Our own Sun is expected
to undergo a similar fate, but fortunately this
will not occur until some 5 billion years from now.

The Hubble image of IC 418 is shown
in a false-color representation, based on Wide Field
Planetary Camera 2 exposures taken in February and
September, 1999, through filters that isolate light
from various chemical elements. Red shows emission
from ionized nitrogen (the coolest gas in the nebula,
located furthest from the hot nucleus), green shows
emission from hydrogen, and blue traces the emission
from ionized oxygen (the hottest gas, closest to
the central star). The remarkable textures seen
in the nebula are newly revealed by the Hubble telescope,
and their origin is still uncertain.